1. Field of the Invention
This invention relates to coal mine roof drilling tools, and particularly to a brazing shim locatable between a drill bit body and a plate-type cutter insert to facilitate a brazing operation between the drill bit body and cutter insert.
2. Description of Prior Developments
U.S. Pat. No. 4,817,742 to H. Whysong shows a drilling tool wherein a U cross-sectioned butterfly shim is interposed between a plate-type cutter insert and a drill bit body to facilitate a brazing operation between the bit body and cutter insert. The shim is formed out of a flat metal sheet, as shown in FIG. 13 of the patent. Prior to the sheet being bent into its U cross-sectional configuration a series of perforations are punched through the sheet surface. The perforations extend through a central region of the sheet from one edge of the sheet to an opposite edge of the sheet, leaving side regions of the sheet unperforated. Perforations at edge areas of the sheet give the sheet edge a sharp jagged profile that can be a problem for a person handling and manipulating the shim during the process of positioning the shim between the bit body and the cutter insert. The sharp jagged edges can puncture or cut into the person's fingers.
The personal injury problem is aggravated by the fact that in some real time situations the entire surface area of the shim is perforated. In such cases the entire edge surface is sharp and jagged.